Effects of temperature on the reproductive physiology of female elasmobranchs: the case of the narrownose smooth-hound shark (Mustelus schmitti).
Elisio, M., Awruch, C. A., Massa, A. M., Macchi, G. J. and Somoza, G. M.
Instituto Nacional de Investigacion y Desarrollo Pesquero, 7600 Mar del Plata, Argentina; Instituto de Investigaciones Marinas y Costeras (CONICET-UNMdP), 7600 Mar del Plata, Argentina. Electronic address: melisio@inidep.edu.ar.
CESIMAR (Centro Para el Estudio de Sistemas Marinos) - CENPAT - CONICET, U9120ACD Puerto Madryn, Argentina; School of Natural Sciences, University of Tasmania, TAS 7001 Hobart, Australia. Electronic address: Cynthia.Awruch@utas.edu.au.
Instituto Nacional de Investigacion y Desarrollo Pesquero, 7600 Mar del Plata, Argentina. Electronic address: amassa@inidep.edu.ar.
Instituto Nacional de Investigacion y Desarrollo Pesquero, 7600 Mar del Plata, Argentina; Instituto de Investigaciones Marinas y Costeras (CONICET-UNMdP), 7600 Mar del Plata, Argentina. Electronic address: gmacchi@inidep.edu.ar.
Instituto Tecnologico de Chascomus (CONICET-UNSAM), B7130IWA Chascomus, Argentina. Electronic address: somoza@intech.gov.ar.
The knowledge of how temperature influences elasmobranchs reproductive physiology allows a better understanding of their reproductive patterns. This study describes the relationship between temperature fluctuations and the plasmatic changes of the sex steroids related to reproduction: testosterone (T), estradiol (E2) and progesterone (P4), throughout the female reproductive cycle of the shark Mustelus schmitti. A total of 123 adult females were bi-monthly sampled in Buenos Aires, Argentina, coastal waters. Bottom temperatures were recorded at each sampling point and blood samples were taken from each female for plasma sex steroids measurement. Sex steroid plasma levels were analyzed in relation with maximum follicular diameter (MFD), uterosomatic index (USI, as indicator of pregnancy) and temperature using Generalized Additive Models. Plasmatic E2 and T increased during follicular growth until MFD reached 1.34 and 1.46 cm, respectively. Peak of T occurred at the follicular stage associated with parturition (MFD, 1.4-1.6 cm), just prior to final maturation and ovulation (MFD, 1.6-2.0 cm). Progesterone significantly increased at this last ovarian phase, while T and E2 decreased. The increase of USI with pregnancy was associated to a decrease in T and mainly E2 levels, while P4 remained unaffected. Prior to ovulation, T plasma levels decreased with temperature below to 13 degrees C and then increased progressively with a pronounced elevation above 17 degrees C, while E2 presented an opposite pattern. Progesterone plasma levels changed with temperature showing a similar pattern to that observed for T. Using M. schmitti shark as model species, this study shows a clear picture of how seawater temperature variations can affect the reproductive physiolology in elasmobranch females. A hypothetical mechanism (based on T elevation driven by temperature increase and its connection by feedback with a P4 rise and parturition/ovulation induction) is proposed as evidence to support that the increase in temperature can trigger reproductive events in elasmobranchs. In addition to its ecological scope, this work contributes to reinforce the relatively scarce general knowledge of elasmobranchs reproductive physiology.
General and Comparative Endocrinology : 113242 (2019)